1. Field of the Invention
The present invention relates to image-taking apparatuses, such as digital cameras and video cameras that are capable of taking moving images or still images.
2. Description of Related Art
In digital cameras, an object image is exposed for the desired period of time onto a solid-state image-pickup element, such as a CCD sensor or CMOS sensor, in response to pressing a release button, and after converting the resulting image signal into a digital signal, predetermined processing such as YC processing is carried out, and an image signal of a predetermined format is obtained. This digital image signal can be recorded in a semiconductor memory. Then, the recorded image signals can be read out at any time and reproduced by displayable or printable signals, or the recorded images can be visualized by outputting them on a monitor.
Known forms of exposing the object image include the following approaches (see Japanese Patent No. 2870234, for example):
(A) RGB (red, green and blue) color filters in which, for example, 2×2 pixels are taken as a group are formed on a solid-state image-pickup element to provide the pixels one by one with wavelength selectivity, and thus the object image is separated into individual red, green and blue images;
(B) the solid-state image-pickup element is not provided with wavelength selectivity, but optical filters provided with wavelength selectivity are inserted into the image-taking optical system, and are switched chronologically; and
(C) a color separation optical system is added behind the image-taking optical system, and an image is picked up by using a different image-pickup element for each wavelength region.
Moreover, image-taking apparatuses are known that have image-pickup regions that are partitioned into the three color components red, green and blue, that are overall very small, and that have a high-level performance (see Japanese Patent Application Laid-Open No. 2001-78212 (corresponds to EP 1067802A3)).
In any of the approaches of the conventional exposure forms (A), (B) and (C), the image-taking optical system is shared for all wavelength regions, so that it is necessary to have a favorable optical performance across the entire visible region. Ordinarily, image-taking optical systems use the refraction of light with optical materials, such as optical glass or optical transparent resins, for the image-forming principle. Since the refractive index depends on the wavelength, an optical design method called color compensation (correction of achromatic aberration) is used to avoid a lowering of the imaging performance. As a result, it is difficult to configure a high-performance image-taking optical system with one lens, so that the miniaturization of the image-taking optical system becomes problematic.
Japanese Patent Application Laid-Open No. 2001-78212 achieves a compact and high-performance image-taking apparatus, but there are cases in which there are differences in the imaging performance of R, G and B light.